1. Field of the Invention
The present invention relates to an abnormal current discriminating method for detecting an arc generation accident, an overload and a short circuit in an AC load circuit for preventing fires or the like due to such electric accident, and more particularly to a method to be utilized as a protective apparatus for an electric circuit for housing including an extension cord, a cord having a tool and a plug socket.
2. Description of the Related Art
The protection of a cord and a load apparatus through an overcurrent or a short-circuit current has conventionally been carried out by a bimetallic breaker or a breaker using an electromagnetic coil for instantaneous cut-off.
In general, an instantaneous cut-off type breaker is constituted to carry out cut-off when a current which is almost ten times as large as a rated current of the breaker or more flows. In the case in which cores come in contact with each other due to a deterioration in the insulation of a cord so that an arc short circuit is caused, a short-circuit current is not continuous but intermittent different from a load current without the flow of an operating current of an instantaneous breaker. In some cases, therefore, the instantaneous breaker is not operated, resulting in a fire.
In order to eliminate such a drawback, there has been developed a breaker for detecting a current waveform peculiar to an arc. The breaker serves to distinguish and detect a current region which is generated by the contact of the cores of a cord and cannot be detected by the instantaneous breaker from a load current through an electronic circuit. However, a current waveform is also recognized as an arc short-circuit current waveform. In some cases, therefore, a malfunction is caused with a general load current waveform.
As a typical phenomenon in which a fire is caused by a short circuit, the cores are short-circuited so that a short-circuit current flows. At this time, the core is molten by a large current on a short-circuit point so that an arc discharge is generated. The arc discharge generates a very high temperature and scatters a hot molten substance such as a core and a surrounding inflammable substance is ignited to cause a fire.
The arc short circuit caused by the contact and melting of the cores is similarly generated in a load apparatus or an interior wiring in addition to a power cord or extension cord. Moreover, there is also a possibility that a micro current might continuously flow to finally generate an arc short circuit due to deterioration in insulation between plug socket blades.
Moreover, in the case in which one of the cores is cut by some stress and the cut portions come in contact with each other by some force, a current flows and an arc discharge is generated on a cut end if a load is connected. Such an arc generation phenomenon is referred to as a series arc because a current path and a load are connected in series. If such a series arc is generated, a fire is sometimes caused by the molten substance scattered through the arc if a load current is large. In the conventional art, however, a phenomenon generated together with a series arc discharge cannot be detected sufficiently. Therefore, it is greatly desired that an effective breaker should be developed.
In consideration of such circumstances, the present invention proposes a method of discriminating without detecting a normal load current an arc short-circuit phenomenon generated together with an arc discharge through the contact of cores in a cord and an interior wiring and a current abnormality of an AC load circuit including a series arc caused in an apparatus cord or the like which has not been detected by an instantaneous breaker, and an abnormal current detecting apparatus which utilize the same method.
Accordingly, it is a first object of the present invention to provide an abnormal current discriminating method in an AC load circuit capable of detecting no normal load current and detecting without error abnormal current such as an arc short-circuit current generated together with an arc discharge phenomena through the contact of cores in a cord and an interior wiring and a series arc caused through the contact of the cores in an apparatus cord or the like which has not been detected by an instantaneous breaker.
Furthermore, it is a second object of the present invention to provide a discriminating method for detecting a short-circuit current occurring without arc phenomena and over load current in an AC load circuit.
Moreover, it is a third object of the present invention to provide an abnormal current detecting apparatus of an AC load circuit for executing the present methods according to the present invention.
In order to attain the first object, the present invention provides an arc current discriminating method in an AC load circuit, comprising the steps of sampling an alternating current flowing to the AC load circuit in a predetermined cycle and converting the alternating current into a digital value corresponding to its instantaneous current to detect a peak value for each half wave, extracting a predetermined transition pattern specified by the combination of fluctuation patterns of peak values of three continuous half waves from the peak value for each half wave which is thus detected and counting up the number of appearances thereof in a restricted predetermined period, and comparing the count value with the predetermined threshold to decide the current to be an arc current when the count value exceeds a predetermined threshold.
In such a method, the predetermined transition pattern to be counted for detecting the arc current is specified by extracting four kinds of fluctuation patterns, that is, no fluctuation to an increase, an increase to no fluctuation, no fluctuation to a decrease, and a decrease to no fluctuation in the peak values of the three continuous half waves. When applying a simpler method according to the present invention, the predetermined transition pattern is specified by two kinds of fluctuation patterns, that is, an increase to a decrease and a decrease to an increase in the peak values of the three continuous half waves.
In such a method, moreover, the predetermined transition pattern can be specified by the fluctuation patterns of the peak values of the three continuous half waves of alternating current flowing to the AC load circuit including positive and negative half waves serially appeared in a time arrangement order, however when applying to an alternating load circuit to which other load current as half wave rectified is added to a normal load current, it is desirable that either positive or negative three continuous half waves of the alternating current is used for extracting the fluctuation patterns of the peak values of the three continuous half waves.
While the unrectified waveform of the alternating current may be subjected to sampling, it is desirable that full wave rectification should be carried out before the sampling process in order to enhance the detecting precision in a peak value.
In the discriminating method according to the present invention, moreover, in order to avoid the erroneous detection of a change in a normal load current, the additional step of comparing a time series array of the transition pattern as extracted with a predetermined load fluctuation pattern, and clearing to reset the count value which is counted up when the time series array is coincident with the predetermined load fluctuation pattern is further included.
Furthermore, if the peak value for each half wave of the alternating current sampled and digitally converted is smaller than a predetermined threshold, that is, the peak value is much smaller than that in the detection range of the arc current and is to be disregarded, it is excluded from the component of the transition pattern and the number of appearances of the transition pattern in the predetermined restricted period is counted up by using a peak value for each half wave of other alternating currents to be a decision object, thereby discriminating an arc current.
The peak value for each half wave of the alternating current can be detected as a maximum value of the alternating current converted into a digital value obtained by detecting a zero cross point of an alternating voltage supplied to the AC load circuit and sampling the alternating current plural times at regular intervals for a period from the zero cross point to a next zero cross point.
In another method, moreover, the peak value for each half wave of the alternating current may be specified by detecting a zero cross point of an alternating voltage supplied to the AC load circuit, sampling the alternating current plural times at regular intervals and converting the alternating current into a digital value for a period from the zero cross point to a next zero cross point, and calculating an average value of a maximum value of the alternating current converted into the digital value and an instantaneous value of at least one alternating current sampled adjacent thereto in a section of the zero cross point.
In a further arc current discriminating method, erroneous detection of an arm current and a normal load waveform can also be prevented.
In such a method, a waveform sharpness (Vmax/VD):Vmax/VD=a maximum value (Vmax) of an alternating current converted into a digital value/{a maximum value (Vmax)xe2x88x92a minimum value (Vmin) in an instantaneous value of at least one sampled alternating current adjacent to the maximum value} which exceeds a predetermined threshold is excluded from the peak value specified by sampling the alternating current and converting the alternating current into a digital value at regular intervals, and the number of appearances of the transition pattern in the predetermined restricted period is counted up by using, as objects, only a peak value for each half wave of other alternating currents, thereby discriminating an arc current.
In another method, moreover, when a time interval between a time that a zero cross point of an alternating voltage supplied to an AC load circuit is detected and the alternating current is sampled plural times at regular intervals and is converted into a digital value for a period from a certain zero cross point to a next zero cross point and a maximum value of the sampled alternating current is obtained and the zero cross point of the alternating voltage exceeds a predetermined threshold, that is, a predetermined phase angle, the detected peak value is excluded and the number of appearances of the transition pattern in the predetermined restricted period is counted up by using a peak value for each half wave of other alternating currents, thereby discriminating an arc current. Consequently, erroneous detection can be prevented from being caused together with a specific load waveform.
In the restricted period in which the number of appearances of the transition pattern is to be counted, a starting point is set to be a time that a first transition pattern to be counted appears.
In the present invention, furthermore, the following method is also applied in order to detect an arc current rapidly.
More specifically, in a method, a starting point of a restricted period in which the number of appearances of the transition pattern to be counted is set to be a time that a first transition pattern to be counted appears, and further if the number of appearances of the transition pattern in the restricted period is less than a predetermined threshold, such starting point of the restricted period is sequentially shifted every half wave, thereby counting the number of appearances of the transition pattern.
In a further method, moreover, when a transition pattern is to be decided based on the fluctuation patterns of the three continuous half waves, at least one peak value used in a previous transition pattern is repeatedly used.
Furthermore, in the present invention, an abnormal current discriminating method for preferably applied to detection of arc short-circuit current which is caused in a larger current range than that of a series arc current is also included. And in such method, an absolute value of the instantaneous value of the detected alternating current is integrated in a predetermined restricted period and then an abnormal current is discriminated by the virtual arc energy value thus integrated.
Namely, such a method is characterized in that an alternating current flowing to the AC load circuit is sampled in a predetermined cycle and is converted into a digital value corresponding to an instantaneous current, then a virtual arc energy is calculated by only simple integrating of an absolute value of an instantaneous value of the current converted into the digital value in a predetermined restricted period, and thereafter it is decided that an abnormal current is generated when the virtual arc energy value thus calculated exceeds a predetermined threshold.
In such a method, moreover, a starting point of the predetermined restricted period is set to be a time that the absolute value of the instantaneous current sampled and digitally converted first exceeds the preset threshold for rapidly discriminating.
Furthermore, an abnormal current discriminating method effective for an arc short-circuit and over load current, of which current ranges are larger than that of virtual arc energy calculation method as mentioned above is further proposed as the present invention, and such method is characterized in that an alternating current flowing to the AC load circuit is sampled in a predetermined cycle, and it is decided that an arc short circuit or another short-circuit current is generated immediately after a value obtained by a conversion into a digital value corresponding to an absolute value of an instantaneous current thus sampled exceeds a predetermined value continuously a predetermined number of times.
There are also proposed a method of concurrently carrying out three kinds of abnormal current discriminating method as mentioned above as the present invention, in which three kind of algorithms for carrying out three kinds of method, namely first to third current discriminating method, are executed by way of inputting alternating current into a current-voltage converting circuit for sampling and digitally converting, of which amplification degree is preset as the same value or as different values according to each of three discriminating methods.
According to the method, in one embodiment, at least one current discriminating method selected from the first to the third current discriminating methods is carried out, and in other embodiment, three kinds of current discriminating method are concurrently carried out in a manner that the data processing for the third current discriminating method is started prior to the data processing for the first and second current discriminating method.
A further abnormal current detecting apparatus is still further proposed as the present invention, the apparatus comprises a current-voltage converting circuit for sampling an alternating current flowing to the AC load circuit in a predetermined cycle and converting the alternating current into a digital value; the amplification degree of circuit being set as the same value or a variable value, a zero cross detecting circuit for detecting a zero cross point of an alternating voltage supplied to the AC load circuit; and a data processing section for executing necessary data processing for carrying out first to third current discriminating methods.
According to the apparatus, in one embodiment, at least one current discriminating method selected from the first to the third current discriminating methods is carried out, and in other embodiment, three kinds of current discriminating method are concurrently carried out in a manner that the data processing for the third current discriminating method is started prior to the data processing for the first and second current discriminating method.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof.